Birds Build Their Songs Using Just Eight Musical Elements, Study Finds

Across the globe, birdsong is stunningly diverse—from the slow trills of a Northern Cardinal, to the flat whistle of a Three-wattled Bellbird, to the chirps and buzzes of a Barn Swallow. Behind this complexity, though, might lie a remarkable simplicity. According to a new study, the songs of most perching birds are built from just eight basic “acoustic motifs”—like up-and-down trills, one-note whistles, or jumbles of “chaotic notes.” Exploring these musical elements, the study captures a big-picture sense of how and why thousands of species sing the way they do. 

The study, published Thursday in the journal Science, pulled recordings of birdsong from community science databases, like iNaturalist and xeno-canto, and analyzed it using machine learning. “I wanted a summary of birdsongs at a global scale,” says lead author Quentin Bacquelé, a bioacoustic researcher at Saint-Étienne University and Montpellier University in France. 

The study’s scope is unprecedented, the authors say. The team analyzed more than 116,000 songs from 3,160 passerine species, the diverse group that includes all songbirds and more than 60 percent of all birdlife. Their analysis revealed the eight “building blocks” that all these birds draw from when they sing: slow, fast, and ultrafast trills; flat, slow-modulated, and fast-modulated whistles; harmonic stacks; and chaotic notes. The Eastern Wood-Pewee’s “pee-ah-wee,” for example, illustrates the slow-modulated whistle, which sounds like a smooth, plaintive curve of sound, with just a gradual pitch change. The Bohemian Waxwing, meanwhile, offers a great case of the ultrafast trill: high-pitched, rapid-fire pulses that blur together.   

So why does a pewee slowly whistle, while a waxwing rapidly trills? What determines how a species builds its song? 

Bacquelé’s team found that when birds sing, they face a trade-off. They can sing complex songs that encode more information but don’t travel as far, or stick to simpler tunes that carry across longer distances. How a species manages that trade-off depends on its social and biological traits, as well as its environment. 

Often, bigger birds favor simpler sounds like flat whistles and slow trills. Meanwhile, motifs like fast, modulated whistles, which are harder to produce, are more common among smaller species, which have smaller beaks and may have more precise muscular control. Equally, birds that sing to each other over longer distances tend to have simpler songs that carry farther. Those singing more at close range prefer faster, more complex motifs—such as the harmonic stacks of American Crows and those ultrafast waxwing trills. Such complex songs are also more common in species whose males mate with multiple females in a breeding season, making competition more fierce. In monogamous species, simpler, less demanding motifs will do. 

And it’s not just the bird that matters—it’s where they sing, too. Sound travels more easily through open space, while dense vegetation limits its transmission. Bacquelé’s team found that birds favor simpler musical elements, with constant or slowly varying sounds, in tropical rainforests. Here, birds tend to have larger territories, and run into each other less—requiring resilient, longer-range songs that carry across long stretches of vegetation. The White Bellbird, for example, is the world’s loudest recorded bird, calling in flat, metallic whistles through the thick foliage of the Amazon.

Different birds use the same approach in other jungles, the team found, from the Yellow-throated Longclaw in the Congo Basin to the Blue-headed Pitta in Borneo. “They’re thousands of kilometers apart, but the same simple patterns are in tropical rainforests on every continent,” Bacquelé says. “Evolution and ecology created the same solutions to the same problem.” 

Meanwhile, complex motifs, like ultrafast trills, are more common in temperate regions like North America’s forests and open country. In these habitats, birds tend to have smaller territories with less dense vegetation, plus shorter breeding periods—so birds favor complex songs that aid courtship and share more information. Think of the bright, cascading, fast-modulated whistles of the Winter Wren, or the chattering, chaotic notes of the Barn Swallow. (To explore more of these patterns, check out the study’s interactive map.) 

Jeff Podos, a bioacoustician at University of Massachusetts Amherst who was not involved with the study, says the research offers a “highly original” framework for interpreting birdsong. “The authors developed a nuanced, analytical approach that embraces the intrinsic complexity of bird songs, which regularly include multiple motifs,” Podos said in an email.

Indeed, the study found that, on average, a given species has five of the eight motifs in its song repertoire. Almost two-thirds of all songs mixed multiple motifs. And while most birds favored a dominant one, others used a more balanced mix.

Beyond birdsong, this new research approach could benefit other types of animal communication research too, Bacquelé suggests, from frogs, to insects, to mammals. It offers a new kind of framework to analyze patterns in animal communication at a global scale.  

For birders, too, thinking about these motifs could help parse what they’re hearing in the field. “When I listen to birds now, I perceive the song a bit differently,” Bacquelé says. “I listen for a chickadee and say, okay, it’s flat whistles, then trills.” By listening for these elements, birders can uncover clues about the bird they’re hearing, such as its size, mating style, and how its song might be adapted to the environment.

From their social lives to the landscapes they belong to, passerine birds vary greatly. And yet they’re all connected: One way or another, they’re all singing from the same songbook.